Tropical Cyclone Rosita

4 - 17 January 1990

Summary

Intensification of the small cyclone, Rosita , was continuously inhibited by vertical shear which contained the major convection westward of the low-level centre. Although cyclone intensity was maintained for only 2.5 days, the low-level circulation was evident for almost 13 days.

Rosita began as a low pressure centre near 12.7°S, 111.7°E at 1800 UTC 4 January. It tracked steadily in a general westerly direction and developed slowly until 0600 UTC 6 January when it slowed and weakened slightly under the influence of an increasing vertical shear. It remained almost stationary until 9 January when it was shunted northwest by a developing ridge in the middle latitudes.

The low appeared very weak and sheared on satellite imagery as it moved equatorward but, by 0600 UTC 10 January, convection redeveloped and consolidated around it during 11 and 12 January as the low began to slowly intensify. Gales had developed around the centre by 1500 UTC 13 January.

Rosita was tracking south-southeast and was still under the influence of vertical shear which had displaced most of the convection to the west of the low-level centre. The cyclone changed direction again around 2100 UTC 14 January and tracked northwest as it weakened to below tropical cyclone intensity. It was tracking around the periphery of the larger tropical cyclone Sam . The remnants of Rosita tracked equator- ward until they had dissipated on 17 January.